The objective of this project is to characterize the genes for two structurally-related, functionally important cell surface antigens, Mac-1 and LFA-1. Mac-1 is associated with or identical to the complement receptor type three for C3bi on macrophages and granulocytes. LFA-1 is important in killer T lymphocyte interactions with target cells and in T helper cell responses. Mac-1 and LFA-1 comprise a family of leukocyte differentiation antigens of Alpha1Beta1 structure, which contain alternative forms of an Alpha subunit of MW = 170,000 or 180,000 noncovalently associated with an identical or highly homologous Beta subunit of MW = 95,000. Presently available conventional and monoclonal antibodies reactive with the isolated Alpha and Beta subunits, as well as further antibodies to be prepared in this study, will be used to assay mRNA by in vitro translation and immunoprecipitation, and to purify specific polysomal mRNA on immunoadsorbent columns. The cDNA will be prepared using immunopurified or size-fractionated mRNA as templates. The cDNA clones will be screened by preferential binding of appropriate probes and positive selection in translation assays. The cDNA's will be used to obtain genomic clones. The number, structure, and chromosomal location of Alpha and Beta genes will be determined. The expression of Alpha chain genes in differing lineages of leukocyte differentiation, and the induction of Mac-1 Alpha and Beta genes during maturation of the M1 myeloid cell line, will be examined at the level of the Alpha and Beta gene promoters and mRNA transcription. From nucleic acid sequences, protein sequences will be deduced of importance for understanding the structural and functional relationship between Mac-1 and LFA-1. Basic knowledge will be obtained about leukocyte differentiation and about the molecular basis of T lymphocyte and macrophage cell-mediated immunity of importance for cancer and immune diseases.